package org.apache.lucene.util.fst;

/**
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import java.io.IOException;

import org.apache.lucene.store.DataInput;
import org.apache.lucene.store.DataOutput;

/**
 * Holds one or two longs for each input term.  If it's a
 * single output, Long is returned; else, TwoLongs.  Order
 * is preseved in the TwoLongs case, ie .first is the first
 * input/output added to Builder, and .second is the
 * second.  You cannot store 0 output with this (that's
 * reserved to mean "no output")!
 *
 * NOTE: the resulting FST is not guaranteed to be minimal!
 * See {@link Builder}.
 *
 * @lucene.experimental
 */

public final class UpToTwoPositiveIntOutputs extends Outputs<Object> {

    public final static class TwoLongs {
        final long first;
        final long second;

        public TwoLongs(long first, long second) {
            this.first = first;
            this.second = second;
            assert first >= 0;
            assert second >= 0;
        }

        @Override
        public String toString() {
            return "TwoLongs:" + first + "," + second;
        }

        @Override
        public boolean equals(Object _other) {
            if (_other instanceof TwoLongs) {
                final TwoLongs other = (TwoLongs) _other;
                return first == other.first && second == other.second;
            } else {
                return false;
            }
        }

        @Override
        public int hashCode() {
            return (int) ((first ^ (first >>> 32)) ^ (second ^ (second >> 32)));
        }
    }

    private final static Long NO_OUTPUT = new Long(0);

    private final boolean doShare;

    private final static UpToTwoPositiveIntOutputs singletonShare = new UpToTwoPositiveIntOutputs(true);
    private final static UpToTwoPositiveIntOutputs singletonNoShare = new UpToTwoPositiveIntOutputs(false);

    private UpToTwoPositiveIntOutputs(boolean doShare) {
        this.doShare = doShare;
    }

    public static UpToTwoPositiveIntOutputs getSingleton(boolean doShare) {
        return doShare ? singletonShare : singletonNoShare;
    }

    public Long get(long v) {
        if (v == 0) {
            return NO_OUTPUT;
        } else {
            return Long.valueOf(v);
        }
    }

    public TwoLongs get(long first, long second) {
        return new TwoLongs(first, second);
    }

    @Override
    public Long common(Object _output1, Object _output2) {
        assert valid(_output1, false);
        assert valid(_output2, false);
        final Long output1 = (Long) _output1;
        final Long output2 = (Long) _output2;
        if (output1 == NO_OUTPUT || output2 == NO_OUTPUT) {
            return NO_OUTPUT;
        } else if (doShare) {
            assert output1 > 0;
            assert output2 > 0;
            return Math.min(output1, output2);
        } else if (output1.equals(output2)) {
            return output1;
        } else {
            return NO_OUTPUT;
        }
    }

    @Override
    public Long subtract(Object _output, Object _inc) {
        assert valid(_output, false);
        assert valid(_inc, false);
        final Long output = (Long) _output;
        final Long inc = (Long) _inc;
        assert output >= inc;

        if (inc == NO_OUTPUT) {
            return output;
        } else if (output.equals(inc)) {
            return NO_OUTPUT;
        } else {
            return output - inc;
        }
    }

    @Override
    public Object add(Object _prefix, Object _output) {
        assert valid(_prefix, false);
        assert valid(_output, true);
        final Long prefix = (Long) _prefix;
        if (_output instanceof Long) {
            final Long output = (Long) _output;
            if (prefix == NO_OUTPUT) {
                return output;
            } else if (output == NO_OUTPUT) {
                return prefix;
            } else {
                return prefix + output;
            }
        } else {
            final TwoLongs output = (TwoLongs) _output;
            final long v = prefix;
            return new TwoLongs(output.first + v, output.second + v);
        }
    }

    @Override
    public void write(Object _output, DataOutput out) throws IOException {
        assert valid(_output, true);
        if (_output instanceof Long) {
            final Long output = (Long) _output;
            out.writeVLong(output << 1);
        } else {
            final TwoLongs output = (TwoLongs) _output;
            out.writeVLong((output.first << 1) | 1);
            out.writeVLong(output.second);
        }
    }

    @Override
    public Object read(DataInput in) throws IOException {
        final long code = in.readVLong();
        if ((code & 1) == 0) {
            // single long
            final long v = code >>> 1;
            if (v == 0) {
                return NO_OUTPUT;
            } else {
                return Long.valueOf(v);
            }
        } else {
            // two longs
            final long first = code >>> 1;
            final long second = in.readVLong();
            return new TwoLongs(first, second);
        }
    }

    private boolean valid(Long o) {
        assert o != null;
        assert o instanceof Long;
        assert o == NO_OUTPUT || o > 0;
        return true;
    }

    // Used only by assert
    private boolean valid(Object _o, boolean allowDouble) {
        if (!allowDouble) {
            assert _o instanceof Long;
            return valid((Long) _o);
        } else if (_o instanceof TwoLongs) {
            return true;
        } else {
            return valid((Long) _o);
        }
    }

    @Override
    public Object getNoOutput() {
        return NO_OUTPUT;
    }

    @Override
    public String outputToString(Object output) {
        return output.toString();
    }

    @Override
    public Object merge(Object first, Object second) {
        assert valid(first, false);
        assert valid(second, false);
        return new TwoLongs((Long) first, (Long) second);
    }
}
